The modulated molecular beam technique is very efficient in studying surface reactions. It has been applied for measuring adsorption-desorption kinetics of a cadmium vapour on small gold particles deposited on a (100) NaCl surface. The modulation of the incident beam at different frequencies reveals the existence of surface reactions with different rates. At low frequencies (< 0.1 Hz) one observes slow reactions related to processes occurring at the periphery or on the surface of the gold particles. Thus it has been proved that a part of the cadmium atoms reaching the gold particles is first adsorbed in the capture areas of those particles on the substrate. Measurement of these capture areas around the gold clusters as a function of their size and the substrate temperature gives the mean diffusion length and the difference between adsorption and diffusion energies of the cadmium atoms on NaCl. The relaxation time of the overall process as a function of substrate temperature gives the desorption energy of cadmium atoms from the gold particles. © 1985.
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